Cavity tuning device



Patented Oct. 15, 1946- FFICE oAviTY TUNING DEVICE Ingo L. Stephan,Delano 0, N. J., assignor, by

mesne assignments, to Philco Corporation, Philadelphia,` Pa., acorporation of Pennsylvania Application December 16, 1943, SerialNo.514,516`

12 Claims. 1

The present invention relates to cavity `tuning devices for ultra-highradio frequency apparatus, and more particularly to a novel apparatusfor compensating for temperatureY variations in a cavity tuning device.

In ultra-high frequency radio systems it is common to utilize resonantcavities. Such resonant cavities may be tuned by various differentarrangements, loutl one of the most satisfactory methods is to utilizean adjustable diaphragm, the position of which may be varied, forexample, by means of an adjustable screw. Such adjustment, however, iscorrect only for a particular temperature and consequently there may besubsequentjexpansion or contraction of the resonant cavity which willchange the resonant frequency thereof. VIn order to keep the resonantfrequency constant, it is therefore desirable to provide somearrangement for compensating for the expansion or contraction resultingfromdiferences of temperature. It is further desirable that thecompensating arrangement shall be simple and compact in theinterests ofspace conservation and facility of manufacture.

With the foregoing in mind, it is an object of the present invention toprovide a novel arrangement for the temperature compensation of a cavitytuning device.

'It is another object of the invention to provide a simple and compactdevice for compensating the effects of temperature on a resonant cavity.

Other and further objects will become apparent by reference to thefollowing description taken `in connection With the accompanyingdrawing, wherein:

Fig. 1 is a plan View of a tuning cavity provided with an arrangementfor introducing compensation for temperature variations, according tothe present invention;

Fig. 2 is an enlarged cross-sectional view of the apparatus taken alongobtuse angularly dis-V placed lines 2-2 of liig.` 1;

Fig. 3 is a plan view of the device with the upper spider or bridge-Workremoved;

' Fig. 4 is a sectional View taken along the lines 4-4 of Fig. 2; and

Fig. 5 is a diagram explanatory of the principles involved in thetemperature compensation arrangement.

Referring to Figs. 1 to 4, it will become apparent that there has beenshown a resonant cavity III having a `body II which is generally ofcup-shaped orshallow cylindrical configuration.

. 2 The body I I is provided with a surrounding flange I2 havingsuitable threaded apertures therein for receiving a number of fasteningscrews or bolts for retaining other cooperating members in position onthe top of the cup-shaped portion of the cavity. Underneath the body IIof the cavity I0 there. may be `provided one or more coupling p stems`I3`andaI4 each of which has threaded portions,` such as I5 and I6, sothat a coaxial cable may be `coupled thereto. .Within the hollow openingin tl'lemembers I3 and I4, there may be provided probes or couplingloops I1 and I8 as seen in Fig. 4. Thus, Where desired, energy may becoupled to the resonant cavity or extracted therefrom in order toindicate the frequency at which the cavity operates.

Immediately abovethe vertical wall portion I9 of the cavity Ill there ispositioned a movable diaphragm 2I which may be provided with a pluralityof concentric corrugatons 22 to permit the central portion thereof to bemoved in the manner of a piston. The outer 'edge of the diaphragm 2Irests upon the vertical walls I9 of the cavity I0. In order to avoiddetuning of the cavity by changes in barometric pressure, thebreather-hole` 30 is provided to insure equality of air pressures insideand outside the cavity. The breather-hole also serves as a drain in theevent that water should accumulate in the cavity due to condensation ofvapors present in theatmosphere. At the center the diaphragm 2l isprovided with a hollow stud 23 secured thereto and providedinternally'with threads for cooperation with an adjusting screw 24. Theadjusting screw 24 has a collar portion 25 which engages a flat`circular area within a corrugated reinforced portion 21 in a supportingspider or bridgefwork member 20.

The bridgework member 2U has a flat upper portion 29 which is supportedsome distance above the diaphragm 2| by a plurality of legs, such as 3!32 and 33, each of which terminates inflatportions 34, 35 and 36provided with suitable apertures `through which screw fastening means,3I may be placed so as to engage threaded openings 38 in'the lowerflange I2 on the resonant cavity body II. In order to increase therigidity of the central area 29 of the spider 20, the sides thereof maybe turned downwardly as may be seen at 39 in Fig. 2. The angularlydisposed legs 3| to 33 are .made relatively rigid by turning up thesidesthereof as` at .4I to form channeled members. Dueto this arrangement ofturning down the edges of the central portion 29 to form thesides vSISI,and turning upwardly the sides 4I on the three angularly arranged legs,it becomes apparent that at each of the junctures of the legs 3l to 33with the at portions 34 to 36 and with the central portion 29 there isprovided a less rigid hinge portion. Such portions are designated byreference characters 42 to 41 in Figs. 1 and 2. The purpose of thisstructure will appear presently. Since the spider 20 will afford littleprotection to the diaphragm 2 l there A against the bottom side of thespider 2U. The

body structure Il together with the diaphragm 2| form the resonantcavity lo which may be tuned to a desired frequency by adjustment of thediaphragm through manipulation of the adjusting screw 24.

In a resonant cavity system such as disclosed, radial expansion orcontraction of the body structure Il tends to cause a change in theresonant -frequency due to the effect of such expansion or contractionupon the magnetic field which predominates in the areas adjacent thecavity wall. Thus expansion of the structure H tends to cause a decreasein resonant frequency, while contraction of structure ll tends to causean increase in resonant frequency. In accordance with the presentinvention this tendency is counteracted, firstly, by constructing themain body H of the cavity of a material having a low coefficient ofexpansion, and, secondly, by causing the central portion of thediaphragm, in the region where the electric field predominates, to moveso as to affect the electric field in a mannerv to prevent or minimizeany change in resonant frequency due to expansion or contraction of bodylI-. Since the electric field is a maximum in the central area of thecavity, upward movement of the central portion of the diaphragm tends toincrease the resonant frequency, while downward movement of said portiontends to decrease the resonant frequency. The movement of the diaphragmis effected by the abovedescribed bridge structure through the medium ofthe connecting screw and its associated spring. To this end the spidermember 20 is constructed of a material having` a relatively highcoefcient of linear expansion. The screw 24 and spring 5| should have anegligible coecient of expansion so as not to interfere with the desiredoperation.

In o-rder to explain the manner in which the spider structure 20produces the desired movement of the diaphragm, reference is made to thesimplified explanatory diagram of Fig. 5. In this figure, it may beassumed that the U-shaped member A represents a cross-section throughthe cavity body ll and that the line B joining the upper ends of theU-shaped member represents the diaphragm 2 I. Since only the expansionor contraction of spider legs will produce movement of the diaphragm,the spider structure may be simplified in the manner shown. The apexofthe triangle formed by the sides C may be said to be a distance Habove the diaphragm B. Now. if the dimensions of the member A remainxed, or relatively xed, then any expansion of the sides C by an amount cwill produce a much greater increase in the distance H by an amount hwhich represents movement of the diaphragm. The amount h which thedistance H is increased is larger than c by an approximate factor of sina Where a is the angle between the side C and the diaphragm or base B.By selecting a material of the appropriate coe'cients of expansion forthe angular member C, different amounts of compensating movement of thediaphragm can be obtained. Moreover, it will be apparent that if theangle a is small the amount of movement of the diaphragm will be large,and such movement will decrease if the angle is increased. Thus theamount of compensation may be varied by varying the angle a.

The reason for the hinge portions 42 to 41, hereinbefore referred to,will now be apparent. These portions permit the desired expansion orcontraction of the spider legs without causing distortion of the spiderstructure. If desired, these portions may be rendered better capable ofthe required hinge action by weakening the metal of said portions.

From the foregoing description it will be seen that by selectingsuitable materials for the component parts and by designing the spiderstructure accordingly, the desired compensation may readily be obtained.For a given material of the cavity body I l, the spider structure shouldbe designed and contructed so to move the diaphragm in a manner tocounteract any change in resonant frequency which would gtherwise becaused by expansion or contraction of body Il,

In one satisfactory embodiment of the device, the adjusting screw 24 wasmade of Invar, an alloy which undergoes negligible expansion withtemperature. With an Invar adjusting screw, the length of the screw maybe regarded, for all practical purposes, as substantially fixed at alltemperatures normally encountered. In this particular embodiment themain cavity structure I l was of steel. Ideally this structure wouldalso have a negligible coefficient of linear expansion, but since Invaris expensive, steel was selected in its place as having a coefficientsufliciently low for the purpose. The spider element 2D was constructedof aluminum, a metal having a coefcient of expansion almost twice thatof steel.

While a preferred embodiment 0f the invention has been shown anddescribed in order to explain the present invention, it of course, willbel understood that I do not wish to be limited thereto since obviouslymodifications and alterations may be made in the instrumentalitiesemployed and in their general arrangement Without departing from thespirit and scope of the invention as set forth in the appended claims.

I claim:

1. In combination with an ultra-high frequency tuning cavity having amovable diaphragm, means for compensating for temperature variations soas to maintain the resonent frequency of said cavity substantiallyconstant, comprising av temperature-responsive expansible andcontractibl'e member mounted on the cavity structure externally thereof,and a connecting element between said member and the movable diaphragm,whereby the latter is moved in response to expansion kor contraction ofsaid member.

2. In combination with an ultra-high frequency tuning cavity having amovable diaphragm, means for -compensating for temperature variations soas to maintain the resonant frequency of said cavity substantiallyconstant, comprisinga bridgelike member mounted on theca'vityjstructureexternally adjacent said movable diaphragm, said member being formedofmaterial having a high coefficient' of expansion, and aconnectingfelement between said member and the movabletdiaphragm,whereby the latter is moved in response to expansio'nor contraction ofsaid member.

' 3. An ultra-high frequency tuning cavity, comprising a .cup-shap'edmember having a'lew-lcoefcient of `exp'ansion;a flexible diaphragmforming a closure member for said cavity, a bridge-like member spanningsaid diaphragm exteriorly of said cavity and secured to the cavitystructure, said bridge-like member being formed of material having ahigh coefcient of expansion, and connecting means between the centralportions of said bridge-like member and said. diaphragm, whereby thediaphragm'is moved in response to expansion of said bridge-like member.

4. An ultra-high frequency tuning cavity, comprising a cup-shaped memberhaving a low coefficient of expansion, a flexible diaphragm forming aclosure member for said cavity, a spider member spanning said diaphragmexteriorly of said cavity and having legs extending at acute angles tothe plane of said diaphragm and secured to the cavity structure, saidspider member being formed of material having a high coefficient ofexpansion, and connecting means between the central portions of saidspider member and said diaphragm, whereby the diaphragm is moved inresponse to expansion of the legs of said spider member.

5. An ultra-high frequency tuning cavity comprising a cup-shaped basemember, afiexible diaphragm cover for said cup-shaped member, abridge-like frame supported above said diaphragm, said frame having arigid central area supported by a plurality of angularly disposed legs,said legs being adapted to expand and contract with temperature changesthereby to move said rigid central area from one plane to another, andmeans interconnecting said diaphragm with said central area.

6. An ultra-high frequency resonant device having a flexible diaphragmwall, a temperatureexpansible framework having a relatively rigidcentral area adapted to be supported parallel to said diaphragm, saidrigid central area being supported by a plurality of legs, theextremities of which are fixed in position, said legs havingintermediate portions arranged at acute angles to said diaphragm andhaving relatively flexible portions interconnecting said intermediateportions with said rigid central area and with the remaining portions ofsaid legs, and means inerconnecting said central area of said frameworkwith said diaphragm.

7. An ultra-high frequency tuning device having a, diaphragm adapted tobe positioned to determine the resonant frequency of said device, adiaphragm positioning apparatus comprising a temperature-expansibleframework having a body supported on a plurality of legs angularlydisposed with respect 'to said diaphragm and said body, said legs beingjoined to said body with portions less rigid than the remaining portionsof said framework whereby said legs may expand and contract withtemperature changes thereby to move said body from one parallel plane toanother, and means interconnecting said diaphragm with said body.

8. An ultra-high frequency tuning device having a movable Wall member, atemperature-exhigh frequency energy into said tuning device.

9. An ultra-high frequency tuning cavity having two spaced apartparalle1 walls, one of said walls being formed of a relatively thinflexible member, means for adjustably positioning said flexible wallwith respect to the other wall compricing a temperature-expansibleframework having a central body portion supported on a plurality of legseach angularly disposed with respect to said body portion, said legsterminating in portions rigidly secured in position with respect to saidother wall of said cavity, said angularly disposed portions of said legsbeing interconnected with the fixed portions of said legs and with saidcentral body portion by relatively flexible portions whereby in responseto temperature changes the expansion or contraction of said angularlydisposed leg portions will cause said body portion to be moved from oneplane to another, an adjustable screw member interconnecting said bodyportion of said framework with said flexible cavity wall whereby saidwall may be adjusted to initially determine the resonant frequency ofsaid cavity, means for frictionally retaining said adjusting screw inadjusted position, and means for introducing 'ultra-high frequencyenergy into said cavity.

10. An ultra-high frequency tuning cavity comprising s, relativelyshallow cylinder having one end formed of a flexible diaphragm, anannular supporting ring mounted on said cavity, a temperature-expansibleframework supported 'from said annular ring comprising a relativelyrigid central body portion, at least three legs flexibly interconnectedwith said central body portion, each of said legs being provided withflexibly interconnected portions adapted to be secured in position onsaid mounting ring, diaphragm adjusting means interconnecting saiddiaphragm and the central body portion of said framework for initiallydetermining the position of said diaphragm, and means for couplingultra-high frequency radio energy to said cavity.

11. An ultra-high frequency tuning cavity comprising a circular framemember having an annular supporting flange on the exterior thereof, acircular flexible diaphragm cover arranged to constitute one wall ofsaid cavity, an annular ring for securing said diaphragm in position,said ring ybeing secured to said annular flange, an apertured protectivecover for said diaphragm secured to said annular ring, atemperatureexpansible framework having a relatively rigid Centralportion provided with an aperture therein, a plurality of fastening legsarranged to be secured to said annular ring, and a plurality ofninterconnecting legs flexibly secured to said fastening legs and to saidcentral body portion, an adjusting screw mounted in the aperture of saidcentral body portion and extending through the aperture in said coverand engaging cooperating means mounted at the center of said diaphragmwhereby said diaphragm may be adjusted to a predetermined selectedposition, spring means in- 7 terposed between said framework and saiddiaphragm for securing said diaphragm in adjusted position, and meansfor introducing ultra-high frequency energy in said tuning cavity.

12. An ultra-high frequency cavity structure, comprising a cup-shapedmember and a, flexible diaphragm secured thereto, said member and saiddiaphragm cooperatively forming a resonant cavity in which the magneticfield of the contained energy predomnates in the areas adjacent thecavity Wall While the electric eld of said 8 energy predominates in thecentral area of the cavity, the resonant frequency of said cavity beingsubject to change by the eiect on the magnetic eld of expansion orcontraction of said cup-shaped member due to temperature changes, andtemperature-responsive means for moving the central portion of saiddiaphragm so as to produce a, compensating eiect on the electric eld andthereby maintain the resonant fre- 10 quency substantially constant.

INGO L. STEPHAN.

Disclaimer V2,409,321.-Iiigo L. Stephan, Delanco, N. J. CAVITY TUNINGDEVICE. Patent dated Oct. 15, 1946. Disclaimer filed Dec. 10, 1947, bythe assignee, Philco Corporation.

Hereb y enters this disclaimer to claim 1 of said Letters Patent.

[Olicial Gazette January 18, 1.948.]

